A catalytic converter has an oxygen sensor in front and behind it. When the vehicle is warm and running in closed loop mode, the upstream oxygen sensor waveform reading should fluctuate. The downstream O2 sensor reading should be fairly steady. The code will trigger the Check Engine light if the readings of the two sensors are similar. This indicates that the converter is not working as efficiently as it should be.
Sunday, February 6th, 2011 AT 12:19 AM